A flat panel display possesses advantages of being ultra thin, power saved and radiation free. It has been widely utilized. A present flat panel display mainly comprises a LCD (Liquid Crystal Display) or an OLED (Organic Light Emitting Display).
An OLED possesses many outstanding properties of self-illumination, no requirement of backlight, high contrast, ultra-thin, wide view angle, fast response, applicability of flexible panel, wide range of working temperature, simpler structure and process. The OLED is considered as next generation flat panel display technology. OLED can be categorized as PM-OLED (Passive matrix OLED) and AM-OLED (Active matrix OLED).
Generally, TFTs (thin film transistor) are utilized in the pixel driving circuit of an AM-OLED. The TFT substrate of AM-OLED requires two kinds of TFTs for driving: switching transistor and driving transistor which need bridge of a GI via (gate isolation via). The GI via requires an extra photolithographic process which comprises manufacture processes of thin film, photo, etching, stripping and etc.
The oxide semiconductor has higher electron mobility (the mobility of the oxide semiconductor is >10 cm2/Vs and the mobility of the amorphous silicon (a-Si) is merely 0.5˜0.8 cm2/Vs) and has simpler manufacture process and higher compatibility with the amorphous silicon process in comparison with the Low Temperature Poly-silicon (LTPS). Therefore, it can be applicable to the skill fields of Liquid Crystal Display, Organic Light Emitting Display, Flexible Display and etc. Because it fits the new generation production lines and the possible applications in displays with Large, Middle and Small sizes. The oxide semiconductor is hot to the research field of the present industry because the great opportunity of application development.
For now, a common oxide semiconducting thin film transistor can be: an oxide semiconducting thin film transistor with Etch Stopper (ES) structure or an oxide semiconducting thin film transistor with Back channel etching (BCE) structure.
At present, the structure with more developments is the ESL (etching stopper layer) structure. In general, the manufacture of ESL requires an extra photolithographic process (including manufacture processes of thin film, photo, etching, stripping and etc) which can cause increase of the manufacture cost and the descending of the yield.
Please refer to FIG. 1 which is a structural diagram of an oxide semiconductor thin film transistor with etching resistance structure according to prior art. An Etch Stopper Layer (ESL) 300 is formed after the formation of the oxide semiconducting layer 100 and before the formation of the metal source/drain electrodes 200 for protecting the oxide semiconducting layer 100 and preventing the damages in the following processes (such as the formation of the metal source/drain electrodes 200). Accordingly, the stability of the oxide semiconducting thin film transistor is promoted. However, an additional photolithographic process is required for forming an etching stopper layer. One photolithographic process comprises manufacture processes of thin film, photo, etching, stripping and etc. The manufacture cost will be enormously increased and then the production yield is descending only because of extra forming one etching stopper layer.